cfg80211: fix can_beacon_sec_chan, reenable HT40

cfg80211: fix can_beacon_sec_chan, reenable HT40

[ upstream commit 09a02fdb919876c01e8f05960750a418b3f7fa48 ]

This follows wireless-testing 9236d838c920e90708570d9bbd7bb82d30a38130
("cfg80211: fix extension channel checks to initiate communication") and
fixes accidental case fall-through. Without this fix, HT40 is entirely
blocked.

Signed-off-by: Mark Mentovai <mark@moxienet.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: stable@kernel.org
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com
Signed-off-by: John W. Linville <linville@tuxdriver.com>